This invention relates to the regulation of fluid flow and, more particularly, to the switching of fluid flow between multiple discrete paths by means of a single valve assembly.
Instruments which rely upon regulated fluid flow are commonly employed in a wide variety of applications, such as sample purification, chemical analysis, clinical assay, and industrial processing. Such instruments typically function through either continuous or pulsed fluid flow. It will be appreciated that a pulsed-flow instrument is any device which operates by alternately maintaining and halting or reversing a flow stream through the device. This may be accomplished by combinations of valves and/or pumps to first initiate the flow and then stop or reverse it.
Very often, pulsed-flow devices require multiple flow paths to operate efficiently. Generally, efficient operation requires combining flow-through components, such as sorbent columns and connective tubing, with terminal components, such as needles, pumps, and drains. Examples of pulsed-flow devices include laboratory water purification systems, syringe-type reagent dispensers, manual and automated solid phase extraction (SPE) instruments, supercritical fluid extraction (SCF) instruments, stopped-flow spectrophotometers, automated protein or nucleic acid sequencers and solid phase protein or nucleic acid synthesizers.
Pulsed-flow instruments can be contrasted with continuous-flow devices which during their normal operation require a constant, unidirectional flow. Continuous-flow instruments also require different flow configurations to prime the system during set up or to perform different methods of analysis. Examples of continuous-flow systems include high pressure liquid chromatographs (HPLC), gas chromatographs (GC), clinical analyzers, and flow-injection analyzers.
For both pulsed- and continuous-flow systems, at least two different flow paths are frequently required to, for example, isolate a component from the flow system, attach a component into the flow system, or rearrange the order of the components in the flow system. For many systems, three or more unique flow paths are necessary for optimum operation.
It is known that combinations of commercially available valves can be arranged to provide an infinite number of flow paths among the flow-through components and terminal components employed in a flow system. There exists the practical problem, however, of connecting the large number of valves required for some flow path combinations, especially when minimum volumes within the flow system are desirable. Another problem involves properly orienting all of the valves so as to allow the desired flow path. It will be appreciated that as additional valves are added to the flow system, solutions to both of these problems both more expensive and complex.
Rotary valve assemblies having more than two flow paths are available in a large variety of configurations. For example, radial valve assemblies such as depicted in FIGS. 1-7 are available from the Hamilton Corporation (Reno, Nev.). The valve assemblies comprise a housing (10) which comprises an outer face (11) and a sleeve (12). A common port (14) extends axially through the outer face and a plurality of peripheral ports (13) extend radially through the sleeve. The valve assemblies further comprise a circular valve plug (20) contained within the housing, having a a body (22) which has an end face (21) and a lateral face (23). Distribution valve assemblies--such as shown in FIGS. 1 and 6--have a circular, pore-like distribution channel (24) contained substantially within the body. Switching valve assemblies--such as shown in FIGS. 2 and 7--have semi-circular or square grooved switching channels (26) on the lateral face.
Another class of radial valve assemblies, depicted in FIGS. 8-13, are available from the Valco Corporation (Houston, Tex.). The valve assemblies comprise a housing (50) which comprises an outer face (51) and a sleeve (52). A common port (54) and a plurality of peripheral ports (53) extend radially through the sleeve. The valve assemblies further comprise a conical valve plug (60) contained within the housing, having a body (62) which has an end face (61) and a lateral face (63). Distribution valve assemblies--such as shown in FIGS. 8, 11, and 12--have a semi-circular or square grooved distribution channel (64) on the lateral face having an axial component (64a) and a radial component (64b). Switching valve assemblies--such as shown in FIGS. 9 and 13--have semi-circular or square grooved switching channels (66) on the lateral face.
An axial valve assembly such as depicted in FIGS. 14-18 is available from the Rheodyne Corporation (Cotati, Calif.). The valve assembly comprises a housing (70) which comprises a sleeve (72) and an outer face (71) in the form of a plate. The outer face comprises a common port (74) and a plurality of peripheral ports (73) extending axially through the entire thickness of the outer face. The valve assembly further comprises a circular valve plug (80) contained within the housing, comprising a body (88) having an end face (86). Distribution valve assemblies comprise semi-circular distribution channels (82) on the end face, while switching valve assemblies comprise switching channels (84) on the end face.
Most commercially-available rotary valves are either distribution type valves or switching (loop) type valves. Distribution valves are characterized by having a single distribution channel which can be turned or otherwise manipulated to connect the common port and any one of the peripheral ports in a point-to-point configuration. Thus, a distribution channel is capable of fluid communication with both the common port and one of the peripheral ports. The number of unique plug orientations for a distribution valve is determined by the number of peripheral ports the valve assembly comprises in addition to the common port. Peripheral ports not connected to the common port are usually excluded from the flow system. Hence, for each unique orientation of the valve plug only a single unique flow path is allowed.
Switching valves are characterized by providing internal connections between multiple, different sets of valve ports. Switching valves have switching channels which can be manipulated to connect two or more peripheral ports. Thus, a switching channel is capable of fluid communication with two or more peripheral ports. Typically, at least one terminal or flow-through component is connected to a switching valve at two peripheral ports. Fluid should flow from one peripheral port of the switching valve to the component and then from the component to the other peripheral port. As a result, components connected to switching valves have markedly different flow path depending on the valve orientation. Generally, switching valves contain half the number of internal channels as they have valve ports. The channels are symmetrically arranged so that only two unique positions of the plug are established. However, for each unique orientation of the valve plug, multiple flow paths through the valve may be allowed.
Combinations of distribution and switching valves are frequently used in pulsed- and continuous-flow systems to create a large variety of flow paths. However, multiple valve implementations involve a large number of external connections which increases the complexity, expense, and physical volume of the flow system. The complexity of such systems also introduces reliability concerns. Also, since these flow systems are typically automated, greater reliability and lower complexity are critical for successful instrument development.
Few examples are available in which a single valve exhibits properties of both a switching valve and a distribution valve. One example is the stream selection valve depicted in FIG. 19, which is available from the Valco Corporation. The purpose of this valve is to divert a single stream to a common outlet while maintaining flow in all the other streams. However, this valve requires 2n+1 ports to achieve a number, n, unique flow paths. It would be of great advantage to provide a valve assembly having fewer ports yet capable of providing more flow paths.